Amino acid derivatives

ABSTRACT

New lactone intermediates useful in the synthesis of peptides are prepared by reacting an Alpha -amino acid with an active carbonyl compound which forms a Schiff&#39;&#39;s base. The latter is treated with a condensing agent so that cyclization occurs and a lactone is formed from which a peptide may be produced by reaction with an amino acid ester and removal of the protecting groups.

United States Patent Bodanszky 5] Apr. 29, 1975 AMINO ACID DERIVATIVES [56] References Cited [75] Inventor: Miklos Bodanszky, Shaker Heights, UNITED STATES PATENTS 01110 3,558,606 1/1971 Tinney 260/2393 T [73] Assignee: E. R. Squibb & Sons, Inc., New

York Primary Examiner-G. Thomas Todd Attor'nqv, Agent, or Firm-Lawrence S. Levinson; [22] 1973 Merle J. Smith; Burton Rodney [2l] Appl. No.: 349,502

Related US Application Data [57] ABSTRACT Division of Sci. NO 98939- Dc:- 1 1970 Newilactone intermediates usefnl in the synthesis abandoned. which is a continuation-in-part of Ser. P p i are Prepared y reactmg an a'ammo and No. 798.791). Fch. I2. 1969. abandoned. which is a with an active carbonyl compound which forms a continuation-impart of Ser. No. 451,609, April 28, Schiffs base. The latter is treated with a condensing l96 u 0 c agent so that cyclization occurs and a lactone is formed from which a peptide may be produced by re- [52] US. Cl. 260/2393 B; 260/293.55 a ti n with an amino acid ester and removal of the [51 1 Int. protecting groups [58] Field of Search 260/2393 T, 239.3 B, 293.55

8 Claims, No Drawings AMINOACID DERIVATIVES Thisapplication is a division of copending application Ser. No; 98,939 filed Dec. 16, 1970, which application is' a continuation-in-part of copending application Ser. No. 798,790, filed Feb. 12, 1969, which in turn is a"continu-ation in-part of application Ser. No. 451,609, filed Apr. 28, 1965, all now abandoned.

This invention relates to new intermediates useful in the synthesis of peptides. More particularly, the invention relates to amino acid derivatives, especially derivatives of a-amino acids, which are simultaneously protected and activated for reaction with other amino acids in the synthesis of peptides.

In the usual synthesis of peptidesJtwo amino acids are joined head to tail", i.e., the carbonyl group of the acid moiety of one amino acid is joined to the amino group of the second amino acid. It is conventional in such a synthesis to protect the reactive amino group of one amino acid with a readily removable protective group such as benzyloxycarbonyl, t-butyloxycarbonyl, phthalyl, tosyl group, etc., so that the amino group does not enter into the reaction. Then the carbonyl group of the same amino acid is activated with another group, e.g., with an azide or with an ester group such as the pnitrophenyl ester, so that the carbonyl group will react with or acylate the amino group of the second amino acid in the presence of the protecting group.

This procedure, it is evident, requires two distinct reactions with two separate compounds in preparation of the one aminoacid for the,ultimate reaction with the secondamino acid. It further requires the combination of two proper groups which will give the desired protection and activation of the particular amino acid involved,

BRIEFSUMMARY OF THE INVENTION It has now been found that a-amino acids can be both protected and activated by reacting the amino acid with a single compound and then forming a lactone. This method and the novel lactones formed thereby form the essence of this invention. These lactones readily, react with a-amino acid esters to form condensation products. from which the protecting-activating moiety is readily removed to leave the desired peptide.

Briefly, the method comprises reacting an a-amino acid with an active carbonyl compound which forms a Schiffs baseand then the Schiffs base is treated with a condensing agent to induce cyclization and yield a lactone of the formula wherein R is the residue of an a-amino acid, R is hydrogen or lower alkyl, and Z taken with N is a heterocyclic ring or a condensed ring system wherein a heterocyclic ring is condensed with a benzene ring.

DETAILED DESCRIPTION OF THE INVENTION Any a-amino acid may be treated according to this invention. This includes the naturally occurring a-amino acids [see for example, Hackhs Chemical Dictionary, 3rd ed. (1944), pages 44-45] as well as a synthetic a-amino acids. Some examples are monoaminocarboxylic aliphatic acids, e.g., glycine, a-aminoheptylic acid, a-aminocaprylic acid, a-aminononylic acid, a-aminodecylic acid, a-aminoundecylic acid, alanine, serine, cysteine, threonine, methionine, valine, leucine, isoleucine; aromatic monoaminomonocarboxylic acids, e.g., phenylalanine, tyrosine, dihydroxyphenylalanine, 3,5-dibromotyrosine, 3- iodotyrosine, 3,5-diiodotyrosine, 3,5,3- triiodotyronine, and thyroxine; monoaminodicarboxylic acids and their amides, e.g., aspartic acid, glutamic acid, asparagine and glutamine; diaminomonocarboxylic acids, e.g., lysine, hydroxylysine, ornithine and arginine; heterocyclic amino acids, e.g., histidine, tryptophane, proline, hydroxyproline, thiolhistidine; diaminodicarboxylic acids, e.g., cystine, lanthionine and djenkolic; as well as a-amino acids of the same type found in special sources, e.g., phenylglycine, butyrine, citrulline, homocystine, hypoglycin A, S-methylcysteine sulfoxide, alliin and canavanine.

Other amino acids are aminomalonic acid, a-aminoadipic acid, a-aminopimelic acid, a-aminosuberic acid, a-aminosebacic acid, B-hydroxyaspartic acid, cystine- B,B-dicarboxylic acid, B-hydroxyglutamic acid, B-methylaspartic acid, B-methylB-hydroxyaspartic acid, B-methylglutamic acid, [3,[3-dimethylaspartic acid, 'y-hydroxyglutamic acid, B,y-dihydroxyglutamic acid, B-phenylglutamic acid, 'y-methyleneglutamic acid, a-aminotricarballyic acid, B-aminoalanine, 'y-aminobutyrine, homoarginine, homocitrulline, a,a-diaminosuccinic acid, a,a'-diaminoglutaric acid, a,a'-diaminoadipic acid, a,a-diaminopimelic acid,

01,01-diamino-B-hydroxypimelic acid, a,a'-diaminosuberi'c acid, a,a'-diaminoazelaic acid, a,a'-diaminosebacic acid a,a'-diaminodecanedicarboxylic acid, a,a-diaminododecanedicarboxylic acid, y-methylproline, pipecolic acid, baikiain, 5-hydropipecolic acid, azetidine-2-carboxylic acid, B-phenylserine, canaline, y-oxalysine, y-hydroxyornithine, and 2-hexosaminic acids. A comprehensive discussion of amino acids, including those mentioned above, is to be found in Chemistry of the Amino Acids, Greenstein 'et al., Vol. III, Wiley, 1961. Other amino acids in addition to those listed above are to be found in this volume but for sake of brevity are not specifically mentioned herein but are included by reference. It is to be understood that the present invention is applicable -to any amino acid.

The amino acid of the formula ITH RCH-CO2H wherein R is the residue of the amino acid is reacted with a carbonyl compound to produce a Schiffs base. These carbonyl compounds are aldehydes or ketones having the structural formula wherein R is hydrogen or a straight or branched chain lower :tlkyl radical of from 1 to 4 carbon atoms, and Z taken with the nitrogen atom to which it is joined (N) is a heterocyclic ring wherein the ring is formed from 5 or 6 atoms or a condensed ring system wherein a heterocyclic ring as previously defined is condensed with a benzene ring.

Examples of suitable aliphatic carbonyl compounds are the following:

a-formyl-N-hydroxysuccinimide N-hydroxy-B-formylpyrrole N-hydroxy-B-formyl-Z,S-dimethylpyrrole 4-acetyl-N-hydroxypiperidine N-hydroxy-3-formylphthalimide The amino acid is reacted with the aldehyde or ketone in an inert solvent, preferably an inert organic solvent such as dimethylformamide, dioxane, pyridine or the like under conventional conditions for forming a Schiffs base. Then, after the Schiffs base has formed, without isolating the base unless desired, a condensing agent is added to the reaction mixture to form the lactone. An alcohol may also be used as the reaction medium in which the Schiffs base is formed, but in this case the solvent must be removed before adding the condensing agent.

Any condensing agent which promotes the formation of acyl esters may be used. These include, for example, dicycloalkylcarbodiimides, e.g., dicyclohexylcarbodiimide; dialkylcarbodiimides, e.g., dipropylcarbodiimide; diarylcarbodiimides, e.g., diphenylcarbodiimide; alkoxyacetylenes, e.g., ethoxyacetylene, diphenylketene, etc. Dicyclohexylcarbodiimide and ethoxyacetylene are preferred. About one mol or more of condensing agent per mol of Schiff's base may be used. A mol ratio of about 1:1 may be used when thecondensing agent is a carbodiimide. An excess of the condensing agent is preferable when other condensing agents are used.

Sufficient time must elapse for the Schiffs base to form before the condensing agent is introduced. The time period may vary within rather broad limits depending upon the particular reactants, but a period of about one hour to about twenty-four hours is generally adequate. Stirring and/or heating will of course accelerate the reaction. Temperatures in the range of about to 60C. may be used.

The cyclization reaction which occurs upon addition of the condensing agent must be effected in an anhydrous medium and the solvent must be one which has no reactive hydroxy or carboxy group. Media such as those named above, except alcohols, may-be used for the cyclization as well. Room temperature up to about 60C. may be used, with a temperature in the lower end of the range preferred for carbodiimides and a temperature at the higher end of the range for alkoxyacetylenes.

According to one modification, the amino acid and aldehyde are dissolved in the solvent and stirred for about 1 hour to 24 hours. Then, without isolating the Schiff's base, or after merely concentrating the solution, the condensing agent is added.

The active lactones of this invention will then react with another amino acid, preferably a simple ester thereof, such as a lower alkyl ester whereupon the ring opens and the amino acid is acylated. Treatment with aqueous acid, e.g., with hydrochloric acid, dilute sulfuric acid or the like, removes the protecting groups and the desired peptide is obtained.

It will be appreciated that the process of this invention is not limited to the formation of dipeptides from monomeric amino acids but applies as well to the formation of polypeptides from reactants having more than one amino acid moiety, e.g., the formation of tripeptides, tetrapeptides, pentapeptides, hexapeptides, octapeptides, decapeptides, etc. When the amino acid used has another reactive functional group elsewhere in the molecule, this may have to be independently protected in the conventional manner.

The following examples illustrate the invention without, however, limiting the same thereto. All temperatures given are in degrees Centigrade.

EXAMPLE I 2-Hydroxy-5-nitrobenzylidene-L-leucine and its Lactone L-Leucine (2.62 g.) and S-nitrosalicylaldehyde (5.0

g.) are added to a mixture of absolute ethanol (750 ml.) and methanol (50 ml.). The mixture is stirred at room temperature for several hours. When all the leucine is dissolved, the solvents are removed in vacuo. The residue extracted with ether, the ether extracts concentrated and diluted with hexane. A crystalline solid separates. It is filtered and washed with hexane. The crude Schiff base (dec. at ca. ll80 completely melting at ca. 200) is used in the cyclization step without additional purification. The benzylidene derivative (1.40 g.) is dissolved in tetrahydrofuran (40 ml.) and dicyclohexylcarbodiimide (1.03 g.) is added to the solution. After about two hours at room temperature, the completion of the reaction is checked with the IR spectrum of a sample (disappearance of the strong band at 4.8 a, corresponding to the CN bond of the diimide, and appearance of the carbonyl band of the active ester at 5.65 a). The by-product, mainly N,N'-dicyclohexylurea, is removed by filtration and washed with tetrahydrofuran (20 ml.). The filtrate and washings are concentrated in vacuo to dryness, the residue is dissolved in ether, and the solution is diluted with hexane. The active ester is obtained in good yield in the form of crystals with strong double refraction. The product has a poorly defined melting point.

The lactone obtained above and glycine ethyl ester are reacted in chloroform. Dilute hydrochloric acid is added to the reaction mixture and L-leucyl glycine ethyl ester is obtained as the product.

EXAMPLE 2 2-Hydroxy-5-chlorobenzylidene-L-alanine lactone 5-Chlorosalicylaldehyde (0.l57 g.) and L-alanine (0.91 g.) are added to dimethylformamide (10 ml.). After 24 hours at room temperature dicyclohexylcarbodiimide (0.206 g.) is added to the solution. The formation of a CO band at 5.65p. reaches its maximum in about 2 hours. The precipitated dicyclohexylurea is removed by centrifugation and the active lactone which has the structural formula H Cl C=N-CHCH O---CO is precipitated by the addition of ether (50 ml.) to the decanted supernatant solution (1R 5.65,u.).

EXAMPLE 3 L-Phenylalanine (0.165 g.) and 3-formyl-N- hydroxyphthalimide (0.19 g.) are suspended in methanol and the mixture is stirred until complete solution occurs; The methanol is removed in vacuo, tetrahydrofuran (3 ml.) and ethoxyacetylene (3 ml.) are added to the residue and the resulting solution is heated to boiling under reflux condenser for one hour. The solvent I and the excess ethoxyacetylene are removed in vacuo, tetrahydrofuran (3 ml.) and ethoxyacetylene (3 ml.) are added to the residue and the resulting solution is heated to boiling under a reflux condenser for one hour. The solvent and the excess ethoxyacetylene are removed in vacuo and the residue is triturated with ether to yield the active lactone (IR 5.6;1.) having the formula L-Serine (0.105 g.) is reacted with a-formyl-N- hydroxysuccinimide (0.15 g.) as described in Example 3. The Schiff base is obtained by removing the solvent and then reacting with ethoxyacetylene to obtain the active lactone (1R 5.6 1.) having the formula o cH on CH N $111 CH co co CH co EXAMPLE 5 L-Glutamine (1.5 g.) and 4-acetyl-N- hydroxypiperidine (1.5 g.) are stirred in ethanol (100 ml.) for 24 hours. The solvent is removed in vacuo and the residue is treated with dicyclohexylcarbodiimide (2.1 g.) in tetrahydrofuran ml.).. After 3 hours at room temperature. the precipitated N,N'- dicyclohexylurea is removed by-centrifugation and the .r r ole Amino Acid Carbonyl Compound 7 L-glycine malondialdehyde 8 L-alanine B-Jetobutyral' 9 ,L-serine l0 L-glycine succindialdchyde supernatant solution, which contains the active lactone having the structural formula C 1-1 CON H C i CH CPI-CH 0 MW co is used for the synthesis of glutaminyl derivatives.

EXAMPLE 6 To a solution of the Schiff base from 2,4-pentadione and methionine having the formula on c N c111 ca-cn' -ca SCH (23.2 g.) in dimethylformamide (200 ml.), dicyclohexylcarbodiimide (21 g.) is added. After two hours at room temperature, the precipitated N ,N dicyclohexylurea is filtered off and the filtrate which contains the active lactone (1R 5.56;.t) having the formula is used in peptide synthesis.

EXAMPLES 7-26 Following the procedure of Example 3, but protecting reactive side chains where necessary and substituting for L-phenylalanine the amino'acid indicated in column 1, and for 3-formyl-N-hydroxyphthalimide the carbonyl compound indicated in column 11, there is obtained the compound (or mixture of compounds) of formula 1 wherein the substituents R, R R R and m wherein R is the residue of an a-amino acid. R is hydrogen or a straight or branched chain alkyl radical of from 1 to 4 carbon atoms, and

2. A compound according to claim 1 wherein is a radical of the formula 3. A compound according to claim 1 wherein is a radical of the formula 4. A method for preparing a compound of claim 1 comprising reacting an a-amino acid of the formula wherein R is the residue of the amino acid with a carbonyl compound of the formula l -N CH R l5 N n o-c'g wherein is as defined in claim 1, the reaction taking place in an inert organic solvent at a temperature of from about 15 to about 60C and then adding a carbodiimide or alkoxyacetylene condensing agent under anhydrous conditions at from about room temperature to about 60C to the Schiffs base to form a lactone.

5. A compound according to claim 2 wherein the amino acid is serine.

6. A compound according to claim 3 wherein the amino acid is glutamine.

7. A method according to claim 4 wherein the amino acid is serine and the' carbonyl compound is a-formyl-N-hydroxysuccinimide.

8. A method according to claim 4 wherein the amino acid is glutamine and the carbonyl compound is 4-acetyl-N-hydroxypiperidine. 

1. A COMPOUND OF THE FORMULA
 2. A compound according to claim 1 wherein
 3. A compound according to claim 1 wherein
 4. A method for preparing a compound of claim 1 comprising reacting an Alpha -amino acid of the formula
 5. A compound according to claim 2 wherein the amino acid is serine.
 6. A compound according to claim 3 wherein the amino acid is glutamine.
 7. A method according to claim 4 wherein the amino acid is serine and the carbonyl compound is Alpha -formyl-N-hydroxysuccinimide.
 8. A method according to claim 4 wherein the amino acid is glutamine and the carbonyl compound is 4-acetyl-N-hydroxypiperidine. 